Running Critical Speed Calculator

About this calculator

Critical speed comes from the hyperbolic critical power model (originally developed by Monod and Scherrer, and widely adapted to running), which splits performance into two components: critical speed, the highest pace a runner can theoretically sustain indefinitely without fatiguing, and D′ (D-prime), a fixed reserve of distance that can be covered above critical speed before exhaustion forces a slowdown.

With two all-out timed efforts over different distances, the two-point method solves for both: critical speed equals the difference in distance divided by the difference in time between the two efforts, and D′ is the distance covered above what critical speed alone would predict. Running coaches and exercise scientists use critical speed similarly to the lactate/anaerobic threshold, and D′ to gauge anaerobic capacity and pacing strategy for middle-distance events. This calculator takes your two distances and times and estimates critical speed and D′.